Sensing device, power reception device, power transmission device, non-contact power transmission system, and sensing method

ABSTRACT

There is provided a sensing device including a circuit including at least a coil electromagnetically coupled to an outside; a temperature detection unit for detecting a temperature of the coil; a sensing unit for measuring a Q value of the circuit; and a correction unit for correcting the Q value measured by the sensing unit based on temperature information detected by the temperature detection unit.

RELATED APPLICATION DATA

This application is a continuation of U.S. patent application Ser. No.13/600,741 filed Aug. 31, 2012, which is a the entirety of which isincorporated herein by reference to the extent permitted by law. Thepresent application claims the benefit of priority to Japanese PatentApplication No. JP 2011-197381 filed on Sep. 9, 2011 in the Japan PatentOffice, the entirety of which is incorporated by reference herein to theextent permitted by law.

BACKGROUND

The present disclosure relates to a sensing device, a power receptiondevice, a power transmission device, a non-contact power transmissionsystem, and a sensing method that sense the presence of a conductor suchas a metal.

Recently, non-contact power transmission systems that supply (wirelesslytransmit) power in a non-contact method have been actively developed.There are roughly two types of techniques among methods of implementingwireless power supply.

One technique is a well-known electromagnetic induction scheme. In theelectromagnetic induction scheme, a degree of coupling between a powertransmission side and a power reception side is very high and power canbe supplied with high efficiency. However, because it is necessary tomaintain a high coupling coefficient between the power transmission sideand the power reception side, power transmission efficiency betweencoils of the power transmission side and the power reception side(hereinafter referred to as “efficiency between coils”) may besignificantly degraded if the power transmission side is distant fromthe power reception side or there is a position gap.

The other technique is referred to as a magnetic-field resonance scheme,and has a characteristic that magnetic flux shared by a power supplysource and a power supply destination may be lower because a resonancephenomenon is actively employed. In the magnetic-field resonance scheme,the efficiency between coils is not degraded if a Q value (qualityfactor) is large even when a coupling coefficient is small. The Q valueis an index representing a relationship between energy retention andloss in a circuit having a coil of the power transmission side or thepower reception side (indicating the strength of resonance of a resonantcircuit). That is, there is a merit in that axial alignment of the coilsat the power transmission side and the power reception side isunnecessary and a degree of freedom of positions or distances of thepower transmission side and the power reception side is high.

In the non-contact power transmission system, one important element is acountermeasure against heat generation of metallic foreign materials.This is not limited to the electromagnetic induction scheme or themagnetic-field resonance scheme. There is a problem in that heat isgenerated due to an eddy current occurring in a metal if the metal isbetween the power transmission side and the power reception side whennon-contact power supply is performed. To suppress this heat generation,many techniques for sensing metallic foreign materials have beenproposed.

For example, a technique of determining the presence/absence of ametallic foreign material by finding a change in a parameter (a current,a voltage, or the like) when the metallic foreign material is putbetween the power transmission side and the power reception side hasbeen proposed. In this technique, it is not necessary to impose designconstraints and it is possible to suppress cost. For example, a methodof detecting a metallic foreign material according to a degree ofmodulation during communication between a power transmission side and apower reception side in Japanese Patent Application Laid-Open No.2008-206231 and a method of detecting a metallic foreign materialaccording to eddy-current loss (foreign-material sensing based on directcurrent (DC)-DC efficiency) in Japanese Patent Application Laid-Open No.2001-275280 have been proposed.

SUMMARY

However, in the techniques proposed in Japanese Patent ApplicationLaid-Open Nos. 2008-206231 and 2001-275280, the effect of a metalhousing of the power reception side is not added. When charging to ageneral portable device is considered, some kind of metal (a metalhousing, a metal component, or the like) is more likely to be used inthe portable device, and it is difficult to distinguish whether a changein a parameter is “a change due to the effect of the metal housing orthe like” or “a change due to the incorporation of a metallic foreignmaterial.” In the example of Japanese Patent Application Laid-Open No.2001-275280, it is difficult to determine whether eddy-current lossoccurs in the metal housing of the portable device or the eddy-currentloss occurs due to the incorporation of the metallic foreign materialbetween the power transmission side and the power reception side.According to the techniques proposed by Japanese Patent ApplicationLaid-Open Nos. 2008-206231 and 2001-275280 as described above, it isdifficult to accurately sense the metallic foreign material.

It is desirable to improve the accuracy of detection of a metallicforeign material between a power reception side and a power transmissionside.

According to an embodiment of the present disclosure, a temperaturedetection unit of a sensing device detects a temperature of a coil to beused for power transmission or power reception, a sensing unit measuresa Q value of a circuit including the coil, and the temperature detectionunit corrects the Q value to be used to detect a metallic foreignmaterial based on temperature information detected by the temperaturedetection unit.

According to another embodiment of the present disclosure, a Q value ofa circuit including a coil is corrected by a variation in a resistancevalue due to an increase in a temperature of the coilelectromagnetically coupled to an outside. That is, the temperature(coil temperature) of the coil can be reflected in the Q value of thecircuit including the coil.

According to the embodiments of the present disclosure described above,it is possible to reflect a temperature (coil temperature) of a coilelectromagnetically coupled to an outside in a Q value of a circuitincluding the coil and improve the accuracy of detection of a metallicforeign material between a power reception side and a power transmissionside.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic circuit diagram illustrating Q-value measurementperformed in a non-contact power transmission system;

FIGS. 2A and 2B are circuit diagrams illustrating other examples ofresonant circuits (parallel resonant circuits);

FIG. 3 is a graph illustrating a measurement result of a coil surfacetemperature in the non-contact power transmission system;

FIG. 4 is a schematic block diagram illustrating an internalconfiguration example of a power reception device (secondary side)including a coil temperature detection function according to anembodiment of the present disclosure;

FIG. 5 is a circuit diagram illustrating an example of a temperaturedetection circuit;

FIG. 6 illustrates a temperature characteristic example of a thermistor;

FIG. 7 is a schematic plan view illustrating an implementation form ofthe thermistor;

FIG. 8 is a schematic block diagram illustrating an internalconfiguration example of a power transmission device (primary side) foruse in the non-contact power transmission system according to anembodiment of the present disclosure;

FIG. 9 is a block diagram illustrating main parts of the internalconfiguration example of the power reception device (secondary side)illustrated in FIG. 4;

FIG. 10 is a flowchart of metallic foreign material detection based on acorrected Q value according to an embodiment of the present disclosure;

FIG. 11 is a graph illustrating an example of a relationship between a Qvalue and efficiency between coils;

FIG. 12 is a graph illustrating an example of a relationship between theQ value and the efficiency between coils in a coupling coefficient of0.01 and an approximated linear expression;

FIG. 13 is a flowchart of a non-contact power transmission system towhich a coil temperature abnormality detection function is addedaccording to an embodiment of the present disclosure;

FIG. 14 is a graph illustrating frequency characteristics of impedancein a serial resonant circuit;

FIG. 15 is a graph illustrating frequency characteristics of impedancein a parallel resonant circuit; and

FIG. 16 is a circuit diagram for calculating a Q value from a ratiobetween a real component and an imaginary component of impedance.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, preferred embodiments of the present disclosure will bedescribed in detail with reference to the appended drawings. Note that,in this specification and the appended drawings, structural elementsthat have substantially the same function and structure are denoted withthe same reference numerals, and repeated explanation of thesestructural elements is omitted.

Description will be given in the following order.

1. Embodiment (Temperature Detection Unit: Example in Which Q Value (andThreshold Value) is Corrected on Basis of Coil Temperature)

2. Others (Sensing Unit: Modified Example)

1. Embodiment Introductory Description

Technology of metallic foreign material detection in the presentdisclosure is a technique of detecting a metallic foreign material usinga change in the above-described Q value. The Q value is an indexrepresenting a relationship between energy retention and loss. Ingeneral, the Q value is used as a value indicating the sharpness(resonance strength) of a peak of resonance of a resonant circuit. Themetallic foreign material is a conductor such as a metal between a powertransmission side (primary side) and a power reception side (secondaryside). The term conductor also includes conductors in a broad sense,that is, semiconductors.

[Principe of Q-Value Measurement]

Here, the principle of Q-value measurement will be described withreference to FIG. 1.

FIG. 1 is a schematic circuit diagram illustrating the Q-valuemeasurement performed in a non-contact power transmission system.

A circuit of a power transmission device 10 illustrated in FIG. 1 is anexample of the most basic circuit configuration illustrating theprinciple of Q-value measurement (in the case of magnetic-fieldcoupling). Although FIG. 1 illustrates a circuit including a serialresonant circuit, a detailed configuration may be implemented in varioustypes if a function of the resonant circuit is provided. A technique ofQ-value measurement of this resonant circuit is also used in a measuringdevice (an inductance, capacitance, and resistance (LCR) meter).

If there is, for example, a metal piece as a metallic foreign materialin the vicinity of a primary-side coil 15 of the power transmissiondevice 10, a line of magnetic force passes through the metal piece andan eddy current occurs in the metal piece. When viewed from theprimary-side coil 15, the eddy current changes a Q value of the primaryside as if a real resistance load is connected to the primary-side coil15 by electromagnetic coupling between the metal piece and theprimary-side coil 15. This Q value is measured, leading to detection ofthe metallic foreign material (an electromagnetic coupling state) in thevicinity of the primary-side coil 15.

The power transmission device 10 includes a signal source 11 includingan alternating current (AC) power supply 12, which generates an ACsignal (sinusoidal wave), and a resistance element 13, a capacitor (alsoreferred to as a condenser) 14, and a primary-side coil 15 (a powertransmission coil as an example of a coil). The resistance element 13 isillustrated as internal resistance (output impedance) of the AC powersupply 12. The capacitor 14 and the primary-side coil 15 are connectedto the signal source 11 so as to form a serial resonant circuit (anexample of a resonant circuit). A capacitance value (C value) of thecapacitor 14 and an inductance value (L value) of the primary-side coil15 are adjusted so that resonance is generated at a frequency desired tobe measured. A power transmission unit including the signal source 11and the capacitor 14 performs non-contact power transmission to anoutside through the primary-side coil 15 using a load modulation schemeor the like.

If a voltage between two ends of the primary-side coil 15 and thecapacitor 14 constituting the serial resonant circuit is set to V1 (anexample of a voltage applied to the resonant circuit) and a voltageacross the primary-side coil 15 is set to V2, the Q value of the serialresonant circuit is expressed as in Expression (1)

$\begin{matrix}{Q = {\frac{V\; 2}{V\; 1} = \frac{2\pi\;{fL}}{r_{s}}}} & (1)\end{matrix}$

r_(s): effective resistance value at frequency f

The voltage V2 is obtained by multiplying the voltage V1 by Q. If themetal piece is in the vicinity of the primary-side coil 15, theeffective resistance value r_(s) increases and the Q value decreases.Because the Q value to be measured (in the electromagnetic couplingstate) changes in a decreasing direction in many cases if the metalpiece is in the vicinity of the primary-side coil 15 as described above,it is possible to sense the metal piece in the vicinity of theprimary-side coil 15 by sensing the above-described change.

Although examples of a connection and an application to the serialresonant circuit have been described with reference to Q-valuemeasurement, other resonant circuits may be used as the resonantcircuit. Circuit examples are illustrated in FIGS. 2A and 2B.

In the example of FIG. 2A, the resonant circuit is configured byconnecting a capacitor 14A to a parallel resonant circuit of a capacitor14B and the primary-side coil 15 in series. In addition, in the exampleof FIG. 2B, the resonant circuit is configured by connecting thecapacitor 14B to a serial resonant circuit of the capacitor 14A and theprimary-side coil 15 in parallel. The Q value is calculated using thevoltage V1 between the primary-side coil 15 and the capacitor 14A andthe voltage V2 across the primary coil 15 obtained from the resonantcircuits illustrated in FIGS. 2A and 2B.

The examples of the serial resonant circuit and the other resonantcircuits described above are illustrated to describe the principle of amethod of sensing the electromagnetic coupling state in the presentdisclosure, and the configuration of the resonant circuit is not limitedto these examples.

Although an example of the resonant circuit of the power transmissiondevice (primary side) has been described, this measurement principle isequally applicable to the resonant circuit of the power reception device(secondary side).

[Overview of Present Disclosure]

It is possible to remove a foreign material with high accuracy,regardless of the electromagnetic induction scheme or the magnetic-fieldresonance scheme, by detecting the metallic foreign material using achange in the Q value described above. However, the detection accuracyis likely to be degraded according to a temperature change of a coilelectromagnetically coupled to an outside in this method. In general, anamount of heat generation of the coil is determined according to thefollowing expression based on Joule's law.W=I ² Rt  (2)

That is, the amount of heat generation of the coil is determined by anamount of current flowing through a resistance component of the coil.Because the non-contact power transmission system is used to supply andcharge power between two devices, a greater current flows during powersupply as compared to a wireless communication system for a purpose ofcommunication. In the non-contact power transmission system compared toother systems, the amount of heat generation of the coil tends toincrease.

FIG. 3 illustrates the measurement result of a coil surface temperature(coil temperature) in the non-contact power transmission system. Anambient temperature of the coil during measurement is 25° C. and acurrent flowing through the coil is 500 mA.

As can be seen from FIG. 3, a current flows through the coil even underan environment in which the ambient temperature is constant, and thetemperature of the coil largely changes according to the passage of timein use.

There is a problem in that among properties of the metal, a resistancevalue of the coil changes if the temperature of the coil changes.Temperature coefficients of main metals are shown in Table 1. Atemperature-specific numeric value represents resistance ρ (10⁻⁸ Ωm).

TABLE 1 Temperature Metal 0° C. 20° C. 100° C. Coefficient Copper Cu1.55 1.72 2.23 0.00439 Silver Ag 1.47 1.62 2.08 0.00415 Gold Au 2.05 2.22.88 0.00405 Zinc Zn 5.5 6.1 7.8 0.00418 Lead Pb 19.2 21.9 27 0.00406Tin Sn 11.5 12.8 15.8 0.00374 Aluminum Al 2.5 2.82 3.55 0.0042 Iron Fe9.8 20 — —

The temperature coefficient indicates a degree of a change in aresistance value of the metal per 1° C. For example, as shown in theexample of a coil of copper generally used, because the temperaturecoefficient is 0.00439, the resistance value of the coil is decreased byabout 0.44% if the temperature is increased by 1° C. That is, assumingthat a change amount of the coil temperature is 100° C. when the coil ofcopper is used, the resistance value of the coil falls by about 44%.

Next, the relationship between the coil temperature and the Q value ofthe coil will be described. In general, the Q value of the coil isexpressed as in the following expression in addition to theabove-described expression.

$\begin{matrix}{Q = {{\frac{1}{R}\sqrt{\frac{L}{C}}} = \frac{\omega\; L}{R}}} & (3)\end{matrix}$

The Q value and the resistance value R have an inversely proportionalrelationship, and the Q value also changes when the resistance value Rchanges. That is, the resistance value R changes according to anincrease in the coil temperature. Accordingly, there is a problem inthat the Q value largely changes and the accuracy of metallic foreignmaterial detection based on the Q value is lost.

Actual results obtained by measuring the Q value of the resonant circuitwhile the coil temperature is caused to be changed for each of thepresence/absence of a magnetic body are shown in Table 2. Each numericvalue in Table 2 is a value in each measured temperature when the Qvalue is measured at a certain frequency. L denotes inductance (H) ofthe coil, Q denotes a Q value, and Rs denotes a resistance value at thefrequency of the coil. Here, the magnetic body is a ferrite materialwith a predetermined thickness laid on the back of a spiral coil.

TABLE 2

As shown in Expression (1), the Q value is a parameter determined by theresistance value Rs (in inverse proportion). Consequently, an increasein the resistance value Rs is equivalent to a decrease in the Q value.As can be seen from Table 2, the Q value changes (decreases) accordingto a change (increase) of a resistance component, regardless of thepresence/absence of the magnetic body, and it can be easily seen thatthe resistance component for a change factor of the Q value is dominant.For example, if there is no magnetic body, a variation in the Q valuefrom −20° C. to 60° C. is substantially equal to about 32% with respectto a temperature coefficient under conditions of a temperaturecoefficient of about 0.4% and a temperature change of 80° C. As shown onthe right of Table 2, differences in items between a temperature of 25°C. and other temperatures are expressed in percentages.

From the above results, a large amount of current flows in thenon-contact power transmission system, heat is generated from the coil,and the resistance value and the Q value are likely to be largelychanged during power supply. This case can become the cause of accuracydegradation if a foreign material is detected by changes of the Q valueand the eddy-current value (see Japanese Patent Application Laid-OpenNo. 2001-275280).

In the present disclosure, the inspection of a metallic foreign materialis performed by reflecting the temperature (coil temperature) of a coilelectromagnetically coupled with an outside in a Q value of a circuitincluding the coil.

Hereinafter, a configuration example for reflecting the coil temperaturein the Q value of the circuit including the coil will be described withreference to FIGS. 4 to 7.

FIG. 4 is a schematic block diagram illustrating an internalconfiguration example of a power reception device (secondary side)including a coil temperature detection function. In this example, thepresence/absence of a metallic foreign material is sensed by a Q-valuedetection unit 38, a coil temperature detection unit 39, and a foreignmaterial determination unit 40 during Q-value measurement. The powerreception device 30 is an example of a sensing device.

For example, the power reception device 30 includes a secondary-sidecoil 31, capacitors 32 and 33, a rectification unit 34, a power supplyunit 35, a power supply control unit 36, a load modulation unit 37, theQ-value detection unit 38 (an example of a sensing unit), the coiltemperature detection unit 39 (an example of a temperature detectionunit), and the foreign material determination unit 40 (an example of acorrection unit and a determination unit).

In the power reception device 30, one ends of the secondary-side coil 31and the capacitor 32 connected in parallel are connected to one end ofthe capacitor 33 which is connected to the secondary-side coil 31 inseries, and thus a resonant circuit is configured. The resonant circuitis connected to the power supply unit 35 via the rectification unit 34.An inductance value (L value) of the secondary-side coil 31 andcapacitance values (C values) of the capacitors 32 and 33 are adjustedso that resonance is generated at a frequency desired to be measured.The power reception unit constituted by the capacitors 32 and 33 and therectification unit 34 performs non-contact power reception from anoutside through the secondary-side coil 31. The rectification unit 34converts an AC induction voltage of the secondary-side coil 31 into a DCvoltage, and supplies the DC voltage to the power supply unit 35.

The power supply unit 35 generates a power supply voltage by adjusting avoltage level of the DC voltage obtained by conversion in therectification unit 34, and supplies power to a load 35A or each block.An example of the load 35A is a capacitor (secondary battery) or anelectronic circuit that processes an electric signal.

The power supply control unit 36 controls the generation of a powersupply voltage or the supply of power to the load 35A or the like in thepower supply unit 35. In addition, the power supply control unit 36controls an operation of the load modulation unit 37.

The load modulation unit 37 performs a load modulation process accordingto control of the power supply control unit 36. Although the Q value maybe measured in the power transmission device (primary side), theprimary-side Q value changes under a condition that the load of thepower reception device 30 (the secondary side) changes duringmeasurement, and an error is generated. Thus, it is desirable to measurea load of the primary side under a condition that the load of thesecondary side is constant.

In this example, the load modulation unit 37 constituted by a resistanceelement 37R and a switching element 37T connected in series is connectedto a previous stage of the power supply unit 35 in parallel. While thepower transmission device measures the Q value, the power supply controlunit 36 receives notification indicating that measurement by the powertransmission device is in progress through a communication unit (notillustrated), and turns on the switch element. The effect of the load35A is suppressed by sufficiently increasing the resistance value of theresistance element 37R compared with the resistance value of the load35A. As described above, the load resistance value of the secondary sidecan be set to be constant when the primary-side Q value is measured bycontrolling the load modulation unit 37 of the previous stage of thepower supply unit 35. Thereby, it is possible to improve the accuracy ofmeasurement of the primary-side Q value. It is possible to use atransistor such as a power MOS transistor for the switching element 37Tas an example.

The Q-value detection unit 38 detects voltages (corresponding tovoltages V1 and V2 of FIG. 2A) at points of two ends of the capacitor33, and outputs the detection results to the foreign materialdetermination unit 40.

The coil temperature detection unit 39 detects a temperature of the coil31 and outputs the detection result to the foreign materialdetermination unit 40. The coil temperature detection unit 39 can beimplemented by a temperature detection circuit using a thermistor as anexample.

An example of the temperature detection circuit using the thermistor isillustrated in FIG. 5.

In this example, a thermistor 39A and a resistance element 39B areconnected in series, the side of the thermistor 39A is connected to apower supply line, and the side of the resistance element 39B isconnected to a ground terminal. A voltage VDD is applied to thetemperature detection circuit. At this time, a voltage Vout output froma connection midpoint between the thermistor 39A and the resistanceelement 39B is measured.

A thermistor characteristic example for the thermistor is illustrated inFIG. 6, and a change amount of the resistance value is determinedaccording to a temperature. Thus, a resistance value of the thermistor39A can be obtained by measuring the voltage Vout of FIG. 5, and atemperature of the thermistor 39A can be detected.

The detection result may be configured to be directly output from thecoil temperature detection unit 39 to the foreign material determinationunit 40 as an analog signal or may be configured to be converted by thecoil temperature detection unit 39 into a digital signal and output tothe foreign material determination unit 40.

When the temperature of the secondary-side coil 31 is measured, thethermistor 39A is arranged to be as near as possible to thesecondary-side coil 31 as illustrated in a thermistor mounting exampleof FIG. 7. In this measurement, a spiral coil wound with a Litz wire isused as an example of the secondary-side coil 31, and a magnetic body 31a of ferrite material with a predetermined thickness is laid on the backof the spiral coil. The thermistor 39A is arranged to abut a part of thesecondary-side coil 31, so that a correct temperature of thesecondary-side coil 31 is acquired.

In this example, the present disclosure is not limited to a negativetemperature coefficient (NTC) thermistor having a characteristic of anNTC. For example, a positive temperature coefficient (PTC) thermistor ofa PTC or a critical temperature resistor (CTR) thermistor, theresistance value of which rapidly decreases at more than a certaintemperature, may be used.

Although a method using the thermistor in this example is adopted tomeasure the coil temperature, other generally well-known methods such asa measurement method using atmosphere pressure and a measurement methodusing infrared light may be used.

Returning to the description of the internal configuration example ofthe power reception device 30 of FIG. 4, the foreign materialdetermination unit 40 corrects the Q value detected by the Q-valuedetection units 38 based on the coil temperature detected by the coiltemperature detection unit 39, and determines the presence/absence ofthe metallic foreign material by comparing the corrected Q value to athreshold value. At this time, it is also preferable to correct thethreshold value based on the coil temperature. If the metallic foreignmaterial is determined to be present, the foreign material determinationunit 40 transmits a control signal for stopping an operation of thepower supply unit 35 to the power supply control unit 36.

[Configuration Example of Non-Contact Power Transmission System]

Next, specific configuration examples of the power transmission device(primary side) and the power reception device (secondary side) accordingto the non-contact power transmission system of the present disclosurewill be described.

In the non-contact power transmission system of the present disclosure,as an example, a Q-value detection function (an example of a sensingunit) is provided in both the power transmission device and the powerreception device, and the coil temperature detection unit is provided inthe power reception device.

(Configuration Example of Power Transmission Device)

First, the power transmission device will be described.

FIG. 8 is a schematic block diagram illustrating an internalconfiguration example of the power transmission device for use in thenon-contact power transmission system. A power transmission device 10Aillustrated in FIG. 8 is a specific configuration example of the powertransmission device 10 illustrated in FIG. 1, and also an example of asensing device. Hereinafter, FIG. 8 will be described based ondifferences from FIG. 1.

The power transmission device 10A includes rectification units 21A and21B, analog-to-digital converters (hereinafter referred to as “ADCs”)22A and 22B, and a main control unit 23 as examples of elementsconstituting the sensing unit. Blocks of the power transmission device10A including the elements constituting the sensing unit operateaccording to power supplied from the signal source 11 or a battery (notillustrated).

The rectification unit 21B converts an AC signal (AC voltage) inputbetween the primary-side coil 15 and the capacitor 14 into a DC signal(DC voltage), and outputs the DC signal (DC voltage). Likewise, therectification unit 21A converts an AC signal (AC voltage) input betweenthe signal source 11 and the capacitor 14 into a DC signal (DC voltage).The DC signals after the conversion are input to the ADCs 22A and 22B.

The ADCs 22A and 22B convert analog DC signals input from therectification units 21A and 21B into digital DC signals, respectively,and output the digital DC signals to the main control unit 23.

The main control unit 23 is an example of a control unit, and, forexample, controls the entire power transmission device 10A including amicro-processing unit (MPU). The main control unit 23 includes functionsas an arithmetic processing unit 23A and a determination unit 23B.

The arithmetic processing unit 23A is a block for performing apredetermined arithmetic process. In this example, the arithmeticprocessing unit 23A calculates a ratio between voltages V1 and V2 fromthe DC signals input from the ADCs 22A and 22B, that is, a Q value, andoutputs the calculation result to the determination unit 23B. Inaddition, the arithmetic processing unit 23A can acquire information (aphysical amount such as a voltage value or a coil temperature) regardingsensing of a metallic foreign material from the power reception side(secondary side), and calculate the Q value of the secondary side basedon the information.

The determination unit 23B compares the calculation result (Q value)input from the arithmetic processing unit 23A to a threshold valuestored in a nonvolatile memory 24, and determines whether or not themetallic foreign material is near based on the comparison result. Inaddition, the determination unit 23B can compare the Q value of theabove-described power reception side to the threshold value, anddetermine whether or not the metallic foreign material is near.

The memory 24 stores a threshold value (Ref Q1) of the Q value of theprimary side measured in advance in a state in which there is nothing inthe vicinity of the primary-side coil 15 or in the primary-side coil 15.In addition, a coupling coefficient between the primary side and thesecondary side is stored. In addition, the memory 24 may store athreshold value of a Q value of the secondary side acquired from thepower reception side (secondary side).

If a metallic foreign material is detected using DC-DC efficiency(efficiency between coils), a threshold value of the efficiency betweencoils is stored in the memory 24.

A communication unit 25 is an example of a primary-side communicationunit to communicate with a communication unit 60 of the power receptiondevice 30A (see FIG. 9) to be described later. For example, informationregarding sensing of a metallic foreign material such as a Q value of aresonant circuit including the secondary-side coil of the powerreception device or the determination result of the presence/absence ofthe metallic foreign material is transmitted and received. In addition,an instruction for generating and stopping an AC voltage is issued tothe signal source 11 according to control of a main control unit 23. Theinstruction may be directly issued from the main control unit 23 to thesignal source 11 without passing through the communication unit 25.

It is possible to use, for example, a wireless local area network (LAN)of Institute of Electrical and Electronics Engineers (IEEE) 802.11,Bluetooth (registered trademark), or the like as a communicationstandard in communication with the power reception device. Theinformation may be configured to be transmitted through the primary-sidecoil 15 and the secondary-side coil of the power reception device.

An input unit 26 generates an input signal corresponding to a user'soperation, and outputs the generated signal to the main control unit 23.

Although the Q-value detection function (sensing unit) is provided inthe power transmission device 10A, the Q-value detection function doesnot have to be provided in the power transmission device 10A if there isthe Q-value detection function in the power reception device.

(Configuration Example of Power Reception Device)

Next, the power reception device will be described.

FIG. 9 is a block diagram illustrating an internal configuration exampleof the power reception device for use in the non-contact powertransmission system. The power reception device 30A illustrated in FIG.9 is a more specific configuration example of the power reception device30 illustrated in FIG. 4 and also an example of a sensing device. Thepower reception device 30A of this example is configured to switch acircuit during power supply and Q-value measurement. Hereinafter, FIG. 9will be described based on differences from FIG. 4.

The power reception device 30A is the same as in FIG. 4 in that thesecondary-side coil 31, the resonant circuit including the capacitors 32and 33, and the rectification unit 34 are provided, and a configurationin which power is supplied to the load 35A is provided.

The other end of the capacitor 33 is connected to one input end of therectification circuit 34, and the other ends of the secondary-side coil31 and the capacitor 32 connected in parallel are connected to the otherinput end of the rectification unit 34.

In addition, a capacitor 41 and a first switch 42 are connected inseries, one end of the capacitor 41 is connected to one output end ofthe rectification unit 34, and one end of the first switch 42 isconnected to the other output end of the rectification unit 34. The oneoutput end of the rectification unit 34 is connected to an input end ofa first regulator 52 via a second switch 43, an output end of the firstregulator 52 is connected to the load 35A, and the other output end ofthe rectification unit 34 is connected to a ground terminal. A secondregulator 53 is also connected to the one output end of therectification unit 34.

The first regulator 52 controls an output voltage or current to beconstant at any time, and supplies a voltage of 5 V to the load 35A asan example. Likewise, the second regulator 53 constantly maintains thevoltage or current, and supplies a voltage of 3 V to each block or eachswitch as an example.

The other end of the capacitor 33 is connected to an AC power supply 70(oscillation circuit) via a third switch 54A, a resistance element 72,and an amplifier 71. In addition, the other end of the capacitor 33 isconnected to an input end of an amplifier 55A via a third switch 54B. Onthe other hand, an input end of an amplifier 55B is connected to the oneend of the capacitor 33 via a third switch 54C. In addition, the otherends of the secondary-side coil 31 and the capacitor 32 connected inparallel are connected to the ground terminal via a third switch 54D.

A switching element such as a transistor or a metal-oxide semiconductorfield-effect transistor (MOSFET) is applied to the first switch 42 (anexample of a first switching unit), the second switch 43 (an example ofa second switching unit), and the third switches 54A to 54D (an exampleof a third switching unit). In this example, the MOSFET is used.

In this example, the amplifiers 55A and 55B, envelope detection units56A and 56B of a subsequent stage, ADCs 57A and 57B, and a main controlunit 58 (an arithmetic processing unit 58A and a determination unit 58B)are provided as an example of a configuration corresponding to theQ-value detection unit 38 (the sensing unit) of FIG. 4.

An output end of the amplifier 55A is connected to the envelopedetection unit 56A. The envelope detection unit 56A detects an envelopeof an AC signal (corresponding to a voltage V1) input from the other endof the capacitor 33 by way of the third switch 54B and the amplifier55A, and supplies a detection signal to the ADC 57A.

On the other hand, an output end of the amplifier 55B is connected tothe envelope detection unit 56B. The envelope detection unit 56B detectsan envelope of an AC signal (corresponding to a voltage V2) input fromthe one end of the capacitor 33 by way of the third switch 54C and theamplifier 55B, and supplies a detection signal to the ADC 57B.

The ADCs 57A and 57B convert analog detection signals input from theenvelope detection units 56A and 56B into digital detection signals,respectively, and output the digital detection signals to the maincontrol unit 58.

The main control unit 58 is an example of a control unit, and, forexample, controls the entire power reception device 30A including anMPU. The main control unit 58 includes functions as the arithmeticprocessing unit 58A and the determination unit 58B. The main controlunit 58 supplies a drive signal to each switch (for example, a gateterminal of the MOSFET) using power supplied from the second regulator53, and controls an ON/OFF operation.

The arithmetic processing unit 58A calculates a ratio between thevoltages V1 and V2 from the detection signals input from the ADCs 57Aand 57B, that is, a Q value, as an example of an element constitutingthe foreign material determination unit 40 of FIG. 4. The Q value iscorrected based on the coil temperature detected in the coil temperaturedetection unit 39, and the corrected Q value is output to thedetermination unit 58B. In addition, a threshold value to be used todetect a metallic foreign material is corrected based on the coiltemperature, and stored in the memory 59. The arithmetic processing unit58A can transmit information (a voltage value or the like) of an inputdetection signal to the power transmission side (primary side) accordingto a setting. Further, a frequency sweep process may be performed duringa process of sensing a metallic foreign material (a sweep processingfunction).

As an example of an element constituting the foreign materialdetermination unit 40 of FIG. 4, the determination unit 58B is a blockthat compares the Q value input from the arithmetic processing unit 58Ato a threshold value stored in the nonvolatile memory 59, and determineswhether or not the metallic foreign material is near based on thecomparison result. As will be described later, measured information canbe transmitted to the power transmission device 10A, and the powertransmission device 10A can calculate the secondary-side Q value anddetermine the presence/absence of the metallic foreign material.

The memory 59 stores a threshold value (Ref Q2) of the secondary-side Qvalue measured in advance in a state in which there is nothing in thevicinity of the secondary-side coil 31 or in the secondary-side coil 31.In addition, the threshold value corrected based on the coil temperaturemay be stored. In addition, a coupling coefficient between the primaryside and the secondary side is stored. In addition, the threshold valueof the primary-side Q value acquired from the power transmission side(primary side) may be stored.

The communication unit 60 is an example of a secondary-sidecommunication unit to communicate with the communication unit 25 of thepower transmission device 10A. For example, information regardingsensing of a metallic foreign material such as a Q value of the resonantcircuit including the secondary-side coil 31 of the power receptiondevice 30A or the determination result of the presence/absence of themetallic foreign material is transmitted and received in thecommunication unit 60. A communication standard applied to thecommunication unit 60 is the same as a communication standard applied tothe communication unit 25 of the power transmission device 10A. Theinformation may be configured to be transmitted via the secondary-sidecoil 31 and the primary-side coil 15 of the power transmission device10A.

An input unit 61 generates an input signal corresponding to the user'soperation, and outputs the generated input signal to the main controlunit 58.

The AC power supply 70 generates an AC voltage (sinusoidal wave) duringQ-value measurement based on a control signal of the main control unit58, and supplies the generated AC voltage to the other end of thecapacitor 33 via the amplifier 71 and the resistance element 72.

The sensing unit of the power reception device 30A configured asdescribed above is controlled by switching of ON/OFF of three switchgroups, that is, the first switch 42, the second switch 43, and thethird switch group 54 (the third switches 54A to 54D). Hereinafter, anoperation of the power reception device 30A will be described focusingon the switching of each switch.

First, power received from the power transmission device 10A accordingto the secondary-side coil 31 is charged in the capacitor 41 (an exampleof an electric storage unit) provided in a subsequent stage of therectification unit 34. A current value and a time operable at powercharged in the capacitor are determined by CV=it.

Here, C denotes electrostatic capacitance of a capacitor, V is a voltagevalue of the capacitor, i denotes a current value of the capacitor, andt denotes time. That is, when a value of a voltage charged in acapacitor of 10 μF changes, for example, from 9 V to 4 V, a current of50 mA can flow for 1 msec. If the electrostatic capacitance value of thecapacitor is large, a larger current can flow or a time for which thecurrent flows can be extended.

However, because an error may occur during communication between thepower reception device 30A and an external device if the capacitor 41having a large electrostatic capacitance value is put in a subsequentstage of the rectification unit 34, it is preferable to perform controlin the first switch 42. That is, a bad effect is eliminated by makingconduction between a drain and a source of the first switch 42 onlyduring Q-value measurement and electrically connecting the capacitor 41.

If the current consumption of the sensing unit is small to a certainextent and a time of Q-value measurement is short, the Q value can bemeasured while a carrier signal from the power transmission device 10Ais stopped. It is necessary to reliably electrically separate a loadfrom the sensing unit when the carrier signal output from the powertransmission device 10A is stopped (during Q-value measurement). Forexample, it is preferable that OFF control be performed if the carriersignal is input to the power reception device 30A using a P-channelMOSFET for the second switch 43 or control be performed using an enablefunction of the first regulator 52. In addition, when charging in thecapacitor 41 is performed or when communication is performed through thecommunication unit 60, there is no problem even when the load isseparated from the sensing unit.

During Q-value measurement, a value of a voltage across the capacitor 33is measured as in a technique of the above-described measuring device(LCR meter). Specifically, the third switches 54A to 54D are turned onat a timing at which the carrier signal has been stopped, and the Qvalue is calculated from two voltage waveforms (voltages V1 and V2)detected at the one end and the other end of the capacitor 33 byrectifying a sinusoidal wave output from the AC power supply 70. Ametallic foreign material is sensed by comparing the calculated Q valueto a preset threshold value.

If no power is supplied from the primary side to the secondary side bycharging power in the capacitor and driving the sensing unit with thepower every time the Q value is measured, the power reception device 30Aof this example can measure the Q value even when the battery of thesecondary side is not used. Therefore, size reduction, weight reduction,and cost reduction of a portable device or the like can be expectedwithout a large size battery for sensing a metallic foreign material atthe secondary side and a complex circuit for controlling power.

In addition, the Q value can be calculated with high accuracy byappropriately switching the third switches 54A to 54D during powersupply and Q-value measurement and preventing interference by a signal(sinusoidal wave signal) for measurement output by the AC power supplyof the secondary side for use in Q-value measurement and a power supplysignal supplied from the primary side.

(Q-Value Correction)

Next, a technique of correcting the Q value will be described.

If the Q value is used to detect the metallic foreign material, the Qvalue may be corrected, for example, according to the followingexpression. The corrected Q value is used to detect the metallic foreignmaterial, thereby improving the accuracy of detection.Corrected Q Value=Q Value at Steady Temperature×{1−(MeasuredTemperature−Steady Temperature)×(Metal Temperature Coefficient)}  (4)

For example, it is assumed that the steady temperature is 25° C., the Qvalue at the steady temperature is 80, and the material of a coil iscopper. At this time, if the measured coil temperature is 100° C., thecorrected Q value is expressed by the following expression.

$\begin{matrix}{{{Corrected}\mspace{14mu} Q\mspace{14mu}{Value}} = {80 \times \{ {1 - {( {100 - 25} ) \times 0.0044}} \}}} \\{= 53.6}\end{matrix}$

FIG. 10 illustrates a flowchart of metallic foreign material detectionby a corrected Q value. Here, the case in which the metallic foreignmaterial is detected by the power reception device 30A will bedescribed.

First, the arithmetic processing unit 58A of the main control unit 58detects the temperature of the secondary-side coil 31 from a voltagevalue output from the coil temperature detection unit 39 (step S1). Inparallel with this, the arithmetic processing unit 58A acquires voltagesV1 and V2 at points of two ends of the capacitor 33 of the resonantcircuit, and detects a Q value (step S2). The arithmetic processing unit58A calculates the corrected Q value using temperature information andQ-value information (step S3).

Here, a threshold value may be corrected according to a coil temperatureand adaptively changed (step S4).

As a first method, a technique in which the arithmetic processing unit58A calls a Q-value threshold value set in consideration of thevariation of the Q value from the memory 59, and calculates a correctedQ-value threshold value based on Expression (4) using the detectedtemperature information is possible. If Expression (4) is used tocorrect the threshold value, “Q Value at Steady Temperature” ofExpression (4) is replaced with “Threshold Value at Steady Temperature.”If the variation is considered as an example, a threshold value of 64 isdrawn by multiplying 80 by a variation of 20%, where 80 is the assumedmedian value (maximum value) of the Q value.

In addition, as a simple technique of correcting the threshold value, amethod in which a threshold value table is registered in the memory 59and the arithmetic processing unit 58A calls an appropriate thresholdvalue from the threshold value table according to the calculatedtemperature information is possible.

As a method of calling the threshold value, for example, a set thresholdvalue is called by dividing a temperature into a plurality of sectionsat predetermined intervals (for example, 5° C. intervals), setting onethreshold value in one section, and associating the threshold value withthe section including a measured temperature. The configuration asdescribed above can reduce a processing load of the arithmeticprocessing unit 58A because a corrected threshold value is obtained byonly calling a corresponding threshold value from the memory 59 based ona coil temperature without correcting the threshold value usingExpression (4) every time metallic foreign material detection isperformed.

After the Q value and the threshold value have been corrected by thearithmetic processing unit 58A, the determination unit 58B compares thecorrected Q value to the corrected threshold value, and determineswhether or not the corrected Q value exceeds the corrected thresholdvalue (step S5).

As a result, a metallic foreign material is determined to be absent fromthe vicinity of the secondary-side coil 31 if the corrected Q value doesnot exceed the corrected threshold value, and the metallic foreignmaterial is determined to be present in the vicinity of thesecondary-side coil 31 if the corrected Q value exceeds the correctedthreshold value.

(Effects)

According to the above-described embodiment, the accuracy of detectionof the metallic foreign material using a Q value is improved because theQ value of a circuit including a coil is corrected by a variation in aresistance value due to an increase in the temperature of the coilelectromagnetically coupled to an outside.

In addition, because it is possible to change a target threshold valueas well as the Q value by following the coil temperature, the accuracyof detection of the metallic foreign material using the Q value isfurther improved.

It is possible to equally improve the accuracy even in a detectiontechnique using efficiency or a technique of finding a change in adegree of modulation as well as the detection of the metallic foreignmaterial using the Q value.

Further, a technique of correcting the Q value according to the coiltemperature of the present disclosure can be utilized, regardless of awireless power supply scheme (an electromagnetic induction scheme or anmagnetic-field resonance scheme), and an additional effect for use inhigh power can be expected.

Modified Example 1

A technique related to Q-value correction of the present disclosure canalso be equally applied to a technique of detecting a metallic foreignmaterial using DC-DC efficiency.

The DC-DC efficiency is determined by integrating circuit efficiency ofrectification or the like with efficiency between coils.“DC-DC Efficiency=Circuit Efficiency at Power Transmission Side×CircuitEfficiency at Power Reception Side×Efficiency between Coils”

Circuit efficiency is mainly produced by power loss in a current flowingthrough ON resistance of a semiconductor. For example, if the circuitefficiency at the power transmission side is 80%, the circuit efficiencyat the power reception side is 80%, and the efficiency between coils is90%, the DC-DC efficiency becomes 0.8×0.8×0.9=57.6%.

Here, the efficiency between coils (logical maximum value) η isexpressed as in the following Expression (5) as is well known.

$\begin{matrix}{\eta = \frac{S^{2}}{( {1 + \sqrt{1 + S^{2}}} )^{2}}} & (5)\end{matrix}$

S is expressed as in the following Expression.S=kQ  (6)Q=√{square root over (Q ₁ Q ₂)}  (7)

Q denotes a Q value of the entire non-contact power transmission system,Q₁ denotes a Q value of the primary side, and Q₂ denotes a Q value ofthe secondary side. That is, in the magnetic-field resonance scheme, theefficiency η between coils is uniquely obtained logically from acoupling coefficient k, which is a degree of electromagnetic coupling ofthe primary-side coil and the secondary-side coil, and a Q value (Q₁) ofthe primary side and a Q value (Q₂) of the secondary side, each of whichis a Q value of a no-load resonant circuit.

As described above, the DC-DC efficiency is correlated with the Q valuesof the primary-side coil and the secondary-side coil.

FIG. 11 illustrates an example of a relationship between a Q value andefficiency between coils in a plurality of coupling coefficients.

As can be seen from FIG. 11, the efficiency between coils changes fromabout 65% to about 45%, for example, if the total Q value changes from100 to 50 when the coupling coefficient k is 0.05. Because this changerate directly affects the DC-DC efficiency, it is possible to improvethe detection accuracy even in the metallic foreign material detectiontechnique based on the DC-DC efficiency by correcting the Q-valuethreshold value.

As a specific correction method, a correction value of the efficiencybetween coils is obtained according to Expression (8) directly usingExpression (7) for obtaining the efficiency between coils.Corrected Efficiency between Coils=(Corrected Primary-Side QValue×Corrected Secondary-Side Q Value×k)²/{1+√(1+Corrected Primary-SideQ Value×Corrected Secondary-Side Q Value×k)}²  (8)

For “Corrected Primary-Side Q Value” and “Corrected Secondary-Side QValue” in Expression (8), it is necessary to provide the coiltemperature detection unit 39 of the power reception side in the powertransmission device 10A when a metallic foreign material is detectedusing the DC-DC efficiency (the efficiency between coils). In addition,a Q-value correction function and a threshold-value correction functionas in the main control unit 58 (the arithmetic processing unit 58A) ofthe power reception device 30A are provided in the main control unit 23(the arithmetic processing unit 23A) of the power transmission device10A.

According to the above-described configuration, the power transmissiondevice 10A corrects the Q value of the primary side based on the coiltemperature, and also the communication unit 25 of the powertransmission device 10A receives the corrected secondary-side Q valuefrom the communication unit 60 of the power reception device 30A.According to Expression (8), the efficiency between coils is correctedand the metallic foreign material is detected using the correctedefficiency between coils. In addition, it is preferable that thethreshold value of the corrected efficiency between coils stored in thememory 24 be corrected based on the coil temperature.

The corrected secondary-side Q value is transmitted from the powerreception device 30A to the power transmission device 10A and thecorrected efficiency between coils is obtained by the power transmissiondevice 10A as described above, and vice versa. That is, the correctedprimary-side Q value may be transmitted from the power transmissiondevice 10A to the power reception device 30A, and the power receptiondevice 30A may correct the efficiency between coils and its thresholdvalue.

Alternatively, measured data (the voltages V1 and V2 and the temperatureof the secondary-side coil) is transmitted from the power receptiondevice 30A to the power transmission device 10A. The power transmissiondevice 10A calculates the secondary-side Q value of the power receptiondevice 30A from the received voltages V1 and V2, corrects thesecondary-side Q value according to the received coil temperature, andobtains the corrected secondary-side Q value. The efficiency betweencoils is corrected using the corrected primary-side Q value and thecorrected secondary-side Q value.

On the other hand, the measured data (the voltages V1 and V2 and thetemperature of the primary-side coil) may be transmitted from the powertransmission device 10A to the power reception device 30A. The powerreception device 30A may calculate the primary-side Q value, thecorrected primary-side Q value, and the corrected efficiency betweencoils.

As described above, it is possible to reduce the processing load of atransmission source by transmitting the measured data (the voltages V1and V2 and the temperature of the coil of the transmission source) andcalculating a corrected Q value of the transmission source orcalculating corrected efficiency between coils in a transmissiondestination.

Alternatively, a method of storing a threshold value for a product of Qvalues of the primary and secondary sides in the memory 59 of the powerreception device 30A or the memory 24 of the power transmission device10A and calling the stored threshold value if necessary is possible.

Further, a correction technique based on a simple approximate expressionaccording to a value of a coupling coefficient is possible.

FIG. 12 illustrates an example of a relationship between the Q value andthe efficiency between coils in a coupling coefficient of 0.01 and anapproximated linear expression. As illustrated in FIG. 11, therelationship between the total Q value and the efficiency between coilsis close to a linear form if the coupling coefficient k is less than orequal to 0.01. That is, correction by a simple linear expression ispossible. The linear expression illustrated in FIG. 12 is an example ofan approximate expression in a coupling coefficient of 0.01, andy=0.19×−1.86.

For example, the improvement of detection accuracy can be expected evenwhen the correction is performed by the simple expression as shown inExpression (9). The steady efficiency between coils is the efficiencybetween coils at the steady temperature. The correction expression isbalanced with a calculation amount, and a load on necessary hardwareincreases when the correction expression is complex. That is, inrelation to the correction, a correct value may be calculated usingExpression (8) or a calculation amount may be reduced using Expression(9). Alternatively, a table in which the corrected efficiency betweencoils is associated with each measured temperature or the like may beprovided in the memory 59, for example, based on Expression (9).Corrected Efficiency between Coils=Value of Efficiency between Coils atSteady Temperature−{0.2×((Temperature Measured at PrimarySide×Temperature Measured at Secondary Side)−Steady Temperature}  (9)

Modified Example 2

A technique related to Q-value correction of the present disclosure isalso applicable to a forced termination process for a power supply orcharging process. That is, a forced termination function when the coiltemperature is abnormal is added to a sensing device.

FIG. 13 is a flowchart of a non-contact power transmission system towhich a coil temperature abnormality detection function is addedaccording to an embodiment of the present disclosure.

First, a threshold value (X value) of a coil temperature is set, and thedetermination unit 58B of the main control unit 58 determines whether ornot the coil temperature exceeds the threshold value (step S11). If thecoil temperature exceeds the threshold value, the power supply orcharging is unconditionally terminated. This is because an abnormalcurrent is likely to flow through the coil when the coil temperatureexceeds the threshold value. If this function is provided in the powerreception device, the power reception device stops a charging operationof the power reception device or causes power supply to be stopped bynotifying the power transmission device of the abnormal coil temperaturethrough the communication unit.

Next, after the coil temperature is determined to be less than or equalto the threshold value, the Q value based on the coil temperature iscorrected according to the above-described Expression (4), and themetallic foreign material is detected according to the corrected Q value(step S12).

In the determination process of step S12, the power supply or chargingis terminated if there is the metallic foreign material. On the otherhand, if there is no metallic foreign material, the power supply by thepower transmission device and the charging by the power reception deviceare performed (step S13).

The power reception device determines whether or not there is a fullcharge at predetermined time intervals (step S14). In the case of thefull charge, a series of processes is terminated. On the other hand, ifthere is no full charge, the process returns to the determinationprocess of step S11 in which it is checked whether or not the coiltemperature is less than or equal to the threshold value. According tothe checked result, the above-described process of steps S12 to S14 isiterated.

As described above, because the metallic foreign material is detectedusing the corrected Q value based on the above-described coiltemperature after the coil temperature is checked to be less than orequal to a given value, a more safe non-contact power transmissionsystem can be established.

2. Others First Example

Although the sensing unit (arithmetic processing unit 23A) of the powertransmission device 10A and the sensing unit (the arithmetic processingunit 58A) of the power reception device 30A obtain a Q value from thevoltage V1 between the capacitor and the coil of the resonant circuitand the voltage V2 across the coil in the above-described embodiment,the Q value may be obtained by a half-power bandwidth method.

If a serial resonant circuit has been configured in the half-powerbandwidth method, the Q value is obtained as in the following Expression(10) from a band (frequencies f1 to f2) serving as impedance that is √2times an absolute value of impedance Z_(peak) at a resonance frequencyf0 as illustrated in the graph of FIG. 14.

$\begin{matrix}{Q = \frac{f_{0}}{f_{2} - f_{1}}} & (10)\end{matrix}$

In addition, when a parallel resonant circuit has been configured, the Qvalue is obtained according to Expression (10) above from the band(frequencies f1 to f2) serving as impedance that is 1/√2 times theabsolute value of the impedance Z_(peak) at the resonance frequency f0as illustrated in the graph of FIG. 15.

Second Example

This example is different from the embodiment. In this example, thearithmetic processing units 23A and 58A calculate a Q value from a ratiobetween a real component and an imaginary component of impedance of theresonant circuit.

In this example, the real component and the imaginary component of theimpedance are obtained using an automatic balancing bridge circuit and avector ratio detector.

FIG. 16 is a circuit diagram of an automatic balancing bridge forcalculating a Q value from a ratio between a real component and animaginary component of impedance.

An automatic balancing bridge circuit 80 illustrated in FIG. 16 has thesame configuration as a generally well-known inverting amplifiercircuit. A coil 82 is connected to an inverting input terminal (−) of aninverting amplifier 83, and a non-inverting input terminal (+) isconnected to the ground. A negative feedback from an output terminal ofthe inverting amplifier 83 to the inverting input terminal (−) isapplied by a feedback resistance element 84. In addition, an output(voltage V1) of an AC power supply 81 for inputting an AC signal to thecoil 82 and an output (voltage V2) of the inverting amplifier 83 areinput to the vector ratio detector 85. The coil 82 corresponds to theprimary-side coil 15 of FIGS. 1 and 8 or the secondary-side coil 31 ofFIGS. 4 and 9.

The automatic balancing bridge circuit 80 operates so that the voltageof the inverting input terminal (−) constantly becomes zero according toa function of the negative feedback. In addition, a current flowing fromthe AC power supply 81 to the coil 82 substantially all flows into thefeedback resistance element 84 because the input impedance of theinverting amplifier 83 is large. As a result, a voltage applied to thecoil 82 is the same as the voltage V1 of the AC power supply 81, andalso the output voltage of the inverting amplifier 83 becomes a productof a current I flowing through the coil 82 and a feedback resistancevalue Rs. This feedback resistance value Rs is a known referenceresistance value. Accordingly, the impedance is obtained by detectingthe voltages V1 and V2 and taking a ratio between the voltages. Becausethe voltages V1 and V2 are obtained as complex numbers, the vector ratiodetector 85 uses phase information of the AC power supply 81 (asindicated by a dashed-dotted line).

In this example, using the automatic balancing bridge circuit 80 and thevector ratio detector 85 as described above, a real component R_(L) andan imaginary component X_(L) of impedance Z_(L) of the resonant circuitare obtained, and the Q value is obtained from a ratio thereof. Thefollowing Expressions (11) and (12) are calculation expressionsexpressing a process of obtaining the Q value.

$\begin{matrix}{Z_{L} = {{R_{L} + {j\; X_{L}}} = {\frac{V\; 1}{I} = {\frac{V\; 1}{V\; 2}{Rs}}}}} & (11) \\{Q = \frac{X_{L}}{R_{L}}} & (12)\end{matrix}$

In the above-described embodiment, the non-contact power transmissionsystem of the magnetic-field resonance scheme has been assumed anddescribed. However, as described above, the present disclosure is notlimited to the magnetic-field resonance scheme, and is also applicableto the electromagnetic induction scheme that suppresses the Q value tobe low by increasing the coupling coefficient k.

In addition, although the coil temperature detection unit is provided inthe power reception device in the embodiment, the coil temperaturedetection unit may be provided in the power transmission device, so that(the main control unit 23 of) the power transmission device may correcta measured Q value or a threshold value based on temperature informationdetected by the coil temperature detection unit.

In addition, although a configuration in which the power transmissiondevice 10A has only the power transmission function and the powerreception device 30A has only the power reception function has beendescribed in the embodiment, the present disclosure is not limitedthereto. For example, the power transmission device 10A may have thepower reception function to receive power from an outside through theprimary-side coil 15. On the other hand, the power reception device 30Amay have the power transmission function to transmit power to an outsidethrough the secondary-side coil 31.

In addition, although an example in which a Q value is measured usinglow power charged in the capacitor 41 of the power reception device 30A(see FIG. 9) has been described in the embodiment, a configuration inwhich the Q value is measured using power of a battery may be madebecause it is preferable that a configuration of a resonant circuit beswitched between a power supply time and a Q-value measurement time. Inthis case, the capacitor 41 is unnecessary.

In addition, although the Q value is measured at the resonance frequencyin the embodiment, a frequency at which the Q value is measured may notnecessarily be consistent with the resonance frequency. Even when the Qvalue is measured using a frequency shifted from the resonance frequencyto an acceptable range, it is possible to improve the accuracy ofdetection of a metallic foreign material between the power transmissionside and the power reception side using the technology of the presentdisclosure.

In addition, although an L value as well as the Q value is changed andthe resonance frequency is shifted by arranging a conductor such as ametal near the primary-side coil or the secondary-side coil, anelectromagnetic coupling state may be sensed with a combination of ashift amount of the resonance frequency due to the changes of the Lvalue and the Q value.

In addition, although the coupling coefficient k also changes when ametallic foreign material is sandwiched between the primary-side coiland the secondary-side coil, the changes of the coupling coefficient kvalue and the Q value may be combined so as to sense the electromagneticcoupling state.

In addition, although an example of coils without cores as theprimary-side coil and the secondary-side coil has been described in theembodiment, a structure of a coil wound around a core having a magneticbody may be adopted.

Further, although an example in which a portable phone is applied to asecondary-side portable device has been described in the embodiment ofthe present disclosure, the present disclosure is not limited to theexample. The present disclosure can be applied to various devices forwhich the power is necessary such as a portable music player and adigital still camera.

Note that the present technology may also be configured as below.

(1) A sensing device comprising:

a circuit including at least a coil electromagnetically coupled to anoutside;

a temperature detection unit for detecting a temperature of the coil;

a sensing unit for measuring a Q value of the circuit; and

a correction unit for correcting the Q value measured by the sensingunit based on temperature information detected by the temperaturedetection unit.

(2) The sensing device according to (1), further comprising:

a determination unit for comparing the corrected Q value to a thresholdvalue and determining that there is a metallic foreign material betweenthe coil and the outside when the corrected Q value exceeds thethreshold value.

(3) The sensing device according to (2),

wherein the correction unit corrects the threshold value based on thetemperature information, and

wherein the determination unit determines that there is a metallicforeign material between the coil and the outside when the corrected Qvalue exceeds the corrected threshold value.

(4) The sensing device according to any one of (1) to (3), wherein thecorrected Q value is obtained as follows:Corrected Q Value=(Q Value at Steady Temperature)×{1−(MeasuredTemperature−Steady Temperature)×(Metal Temperature Coefficient)}.(5) The sensing device according to any one of (1) to (3), wherein thecorrected threshold value is obtained as follows:Corrected Threshold Value=(Threshold Value at SteadyTemperature)×{1−(Measured Temperature−Steady Temperature)×(MetalTemperature Coefficient)}.(6) The sensing device according to any one of (1) to (5), whereinefficiency between the coils after the correction is obtained using thecorrected Q value as follows:

Corrected Efficiency between Coils=(Corrected Primary-Side QValue×Corrected Secondary-Side Q Value×k)²/{1+√(1+Corrected Primary-SideQ Value×Corrected Secondary-Side Q Value×k)}², where k denotes acoupling coefficient.

(7) The sensing device according to (6), wherein, when the couplingcoefficient is small, the efficiency between the coils after thecorrection is approximated as follows:Corrected Efficiency between Coils=Value of Efficiency between Coils atSteady Temperature−{0.2×√(Temperature Measured at PrimarySide×Temperature Measured at Secondary Side)−Steady Temperature}.(8) The sensing device according to any one of (2) to (7), comprising:

a memory for storing the threshold value,

wherein the determination unit reads the threshold value stored in thememory, and compares the read threshold value to the corrected Q value.

(9) The sensing device according to any one of (1) to (8), furthercomprising:

a control unit for stopping electromagnetic coupling between the coiland the outside when the temperature of the coil detected by thetemperature detection unit exceeds a predetermined value.

(10) The sensing device according to any one of (1) to (9),

wherein the temperature detection unit is configured using a thermistor,and

wherein the sensing unit acquires a voltage value corresponding to thetemperature of the coil from the temperature detection unit and detectsthe temperature of the coil using the voltage value.

(11) A power reception device comprising:

a coil to be used for power reception from an outside;

a circuit including at least the coil;

a temperature detection unit for detecting a temperature of the coil;

a sensing unit for measuring a Q value of the circuit; and

a correction unit for correcting the Q value measured by the sensingunit based on temperature information detected by the temperaturedetection unit.

(12) A power transmission device comprising:

a coil to be used for power transmission to an outside;

a circuit including at least the coil;

a temperature detection unit for detecting a temperature of the coil;

a sensing unit for measuring a Q value of the circuit; and

a correction unit for correcting the Q value measured by the sensingunit based on temperature information detected by the temperaturedetection unit.

(13) A non-contact power transmission system comprising:

a power transmission device for wirelessly transmitting power; and

a power reception device for receiving the power from the powertransmission device,

wherein at least one of the power transmission device and the powerreception device includes

a coil electromagnetically coupled to an outside,

a circuit including at least the coil,

a temperature detection unit for detecting a temperature of the coil,

a sensing unit for measuring a Q value of the circuit, and

a correction unit for correcting the Q value measured by the sensingunit based on temperature information detected by the temperaturedetection unit.

(14) A sensing method comprising:

detecting, with a temperature detection unit, a temperature of a coil tobe used for power transmission or power reception;

measuring, with a sensing unit, a Q value of a circuit including thecoil; and

correcting the Q value measured by the sensing unit based on temperatureinformation detected by the temperature detection unit.

Although the series of processes in the above-described embodiment canbe executed by hardware, some processes can also be executed bysoftware. When some processes of the series of processes are executed bythe software, the processes are executable by a computer in which aprogram constituting the software is incorporated into dedicatedhardware or a computer in which a program for executing variousfunctions is installed. For example, the processes may also be executedby installing a program constituting desired software in ageneral-purpose personal computer or the like.

In addition, a recording medium recording program codes of software forimplementing the functions of the above-described embodiment may besupplied in a system or a device. In addition, of course, the functionsare implemented even when a computer (or a control device such as acentral processing unit (CPU)) in the system or the device reads andexecutes the program codes stored in the recording medium (a memory orthe like).

In this case, as the recording medium for supplying the program codes,for example, a flexible disk, a hard disk, an optical disc, amagneto-optical disc, a compact disc read only memory (CD-ROM), acompact disc recordable (CD-R), a magnetic tape, a nonvolatile memorycard, a ROM, and the like can be used.

In addition, the functions of the above-described embodiments areimplemented by executing the program codes read by the computer. Inaddition, an operating system (OS) or the like operating on the computerexecutes all or some of actual processes based on instructions of theprogram codes. The present disclosure also includes the case in whichthe functions of the above-described embodiments are implemented by theprocesses.

In addition, in this specification, processing steps describing atime-oriented process include a process to be executed in time series inthe described order and processes (for example, parallel processing orobject-oriented processing) to be executed in parallel or separatelyinstead of being executed in time series.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

That is, because the above-described embodiments are preferred specificexamples of the present disclosure, various technically preferablelimitations are imposed thereon. However, it is appreciated that thescope of the present disclosure is not limited to these embodimentsunless it is described that they impose limitations on the presentdisclosure. For example, material types, their amounts, processingtimes, processing orders, and numeric conditions of parameters describedin the above are merely preferred examples. In addition, dimensions,shapes, and arrangements in the drawings used to describe theembodiments are also schematically illustrated.

The present disclosure contains subject matter related to that disclosedin Japanese Priority Patent Application JP 2011-197381 filed in theJapan Patent Office on Sep. 9, 2011, the entire content of which ishereby incorporated by reference.

What is claimed is:
 1. A sensing device comprising: a circuit includinga coil that can be electromagnetically coupled to another coil outsideof the circuit and a capacitor; a temperature measuring unit thatmeasures a temperature of the coil; a sensing unit that measures ameasured Q value of the circuit; a correction unit that generates atemperature-corrected measured Q value using the temperature measured bythe temperature measuring unit; and a determination unit that comparesthe temperature-corrected measured Q value with a threshold Q value anddetermines the presence or absence of a metallic foreign material,wherein, the threshold Q value is either (a) a predetermined Q valuecorresponding to a Q value for the circuit when the metallic foreignmaterial is not proximate the sensing unit, or (b) atemperature-corrected predetermined Q value corresponding to the Q valuefor the circuit when the metallic foreign material is not proximate thesensing unit.
 2. The sensing device of claim 1, wherein the threshold Qvalue is the predetermined Q value corresponding to the Q value for thecircuit when the metallic foreign material is not the sensing unit. 3.The sensing device of claim 1, wherein the threshold Q value is thetemperature-corrected predetermined Q value corresponding to the Q valuefor the circuit when the metallic foreign material is not proximate thesensing unit.
 4. The sensing device of claim 1 or 2, wherein thedetermination unit determines the presence of the metallic foreignmaterial when the temperature-corrected measured Q value exceeds thethreshold Q value.
 5. The sensing device of claim 1 or 3, where thedetermination unit determines the presence of the metallic foreignmaterial when the temperature-corrected measured Q value exceeds thetemperature-corrected predetermined Q value.
 6. The sensing device ofclaim 1 or 2, wherein the temperature-corrected measured Q value issubject to a relationship:temperature-corrected measured Q Value=(Q value at steadytemperature)×{1−(measured temperature−steady temperature)×(metaltemperature coefficient)}, where, steady temperature means apredetermined temperature, and metal temperature coefficient is atemperature coefficient for a metal of which the coil is made.
 7. Thesensing device of claim 1 or 3, wherein the temperature-correctedpredetermined threshold value is subject to a relationship:temperature-corrected predetermined Q value=(predetermined Q value atsteady temperature)×{1−(measured temperature-steady temperature)×(metaltemperature coefficient)}, where, steady temperature means apredetermined temperature, and metal temperature coefficient is atemperature coefficient for a metal of which the coil is made.
 8. Thesensing device of claim 1, wherein a corrected efficiency between thecoils after generation of the temperature-corrected Q value is subjectto a relationship:corrected efficiency between coils=(corrected primary-side QValue×corrected secondary-side Q value×k)2/{1+√(1+corrected primary-sideQ value×corrected secondary-side Q value×k)}2, where, k denotes acoupling coefficient, the corrected primary side Q value is the Q valuefor the primary coil as corrected for coil temperature thereof, and thecorrected secondary side Q value is the Q value of the secondary coil ascorrected for coil temperature thereof.
 9. The sensing device of claim1, wherein, given a coupling coefficient between the primary andsecondary coils that is sufficiently small, the efficiency of the coilsafter the correction for coil temperatures is approximately subject to arelationship as follows:corrected efficiency between the coils=value of efficiency between thecoils at steady temperature−{0.2×√(temperature at primarycoil×temperature measured at Secondary coil)−steady temperature}, where,steady temperature is a predetermined temperature.
 10. The sensingdevice of claim 1, further comprising a memory for storing the thresholdQ value, wherein the determination unit reads the threshold Q valuestored in the memory, and then compares the threshold Q value to thecorrected measured Q value.
 11. The sensing device of claim 1, furthercomprising a control unit for stopping electromagnetic coupling betweenthe coil and the outside when the temperature of the coil measured bythe temperature measuring unit exceeds a predetermined value.
 12. Thesensing device of claim 1, wherein: the temperature measuring unit usesa thermistor, and the sensing unit acquires a voltage valuecorresponding to the temperature of the coil from the temperaturemeasuring unit and measures the temperature of the coil using thevoltage value.
 13. A power reception device comprising: a circuitincluding a coil that electromagnetically receives power from outsidethe circuit and a capacitor; a temperature measuring unit that measuresa temperature of the coil; a sensing unit that measures a measured Qvalue of the circuit; a correction unit that generates atemperature-corrected measured Q value using the temperature measured bythe temperature measuring unit; and a determination unit that comparesthe temperature-corrected measured Q value with a threshold Q value anddetermines the presence or absence of a metallic foreign material,wherein, the threshold Q value is either (a) a predetermined Q valuecorresponding to a Q value for the circuit when the metallic foreignmaterial is not proximate the sensing unit or (b) atemperature-corrected predetermined Q value corresponding to the Q valuefor the circuit when the metallic foreign material is not proximate thesensing unit.
 14. A power transmission device comprising: a circuitincluding a coil that electromagnetically transmits power to an outsideof the circuit and a capacitor; a temperature measuring unit thatmeasures a temperature of the coil; a sensing unit that measures ameasured Q value of the circuit across the capacitor; a correction unitthat generates a temperature-corrected measured Q value using thetemperature measured by the temperature measuring unit; and adetermination unit that compares the temperature-corrected measured Qvalue with a threshold Q value and determines the presence or absence ofa metallic foreign material, wherein, the threshold Q value is either(a) a predetermined Q value corresponding to a Q value for the circuitwhen the metallic foreign material is not proximate the sensing unit or(b) a temperature-corrected predetermined Q value corresponding to the Qvalue for the circuit when the metallic foreign material is notproximate the sensing unit.
 15. A non-contact power transmission systemcomprising (a) a power transmission device for wirelessly transmittingpower; and (b) a power reception device for receiving the power from thepower transmission device, one of the power transmission device or thepower reception device including: a circuit with a coilelectromagnetically coupled to another coil in the other of the powerreception device or the power transmission device and a capacitor; atemperature measuring unit that measures a temperature of the coil; asensing unit that measures a measured Q value of the circuit across thecapacitor; a correction unit that generates a temperature-correctedmeasured Q value using the temperature measured by the temperaturemeasuring unit; and a determination unit that compares thetemperature-corrected measured Q value with a threshold Q value anddetermines the presence or absence of a metallic foreign material,wherein, the threshold Q value is either (a) a predetermined Q valuecorresponding to a Q value for the circuit when the metallic foreignmaterial is not proximate the sensing unit or (b) atemperature-corrected predetermined Q value corresponding to the Q valuefor the circuit when the metallic foreign material is not proximate thesensing unit.
 16. A sensing method comprising: providing a circuitincluding (a) a coil that can be electromagnetically coupled to anoutside of the circuit and a capacitor, (b) a temperature measuring unitthat can measure a temperature of the coil, (c) a sensing unit that canmeasure a measured Q value of the circuit across the capacitor, (d) acorrection unit that can generate a temperature-corrected measured Qvalue using the temperature measured by the temperature measuring unit,and (e) a determination unit that can compare the temperature-correctedmeasured Q value with a threshold Q value and determine the presence ofa metallic foreign material, the method comprising the steps of:measuring the temperature of the coil with the temperature measuringunit; measuring the measured Q value of the circuit with the sensingunit; generating the temperature-corrected Q value for the circuit withthe correction unit; comparing the temperature-corrected Q value and thethreshold Q value with the determination unit; and determining with thedetermination unit the presence of the metallic foreign material whenthe temperature-corrected Q value exceeds the threshold Q value,wherein, the threshold Q value is either (a) a predetermined Q valuecorresponding to a Q value for the circuit when the metallic foreignmaterial is not proximate the sensing unit or (b) atemperature-corrected predetermined Q value corresponding to the Q valuefor the circuit when the metallic foreign material is not proximate thesensing unit.
 17. The method of claim 14, wherein the determination unitdetermines that the metallic foreign material is sufficiently proximatethe sensing device when the temperature-corrected measured Q valueexceeds the temperature-corrected predetermined Q value.